Electronic systems are formed using integrated circuits or semiconductor chips commonly fabricated using metal-oxide-silicon field effect transistor (MOSFET) devices. A MOS transistor is four-terminal device with source, drain, gate and body terminals. The gate terminal is typically formed using a gate conductor layer (metal or polysilicon) that is insulated from the body by a gate dielectric layer. The gate dielectric layer is typically a silicon dioxide layer (referred to as “gate oxide layer”). The thickness of the gate oxide layer along with transistor geometry in a given process are some of the factors determining the speed of operation of a transistor device. The thickness of the gate oxide layer and transistor geometry also limit the amount of voltage that can be applied to the transistor device.
Electronic systems with integrated circuits that are operated at high speed often consume large amount of power and generate large amount of heat. In order to reduce the power consumption and achieve high speed, small geometry transistor devices are preferred. Small geometry transistor devices generally use a thinner gate oxide and require a lower power supply voltage to operate. However, many system applications have standard system power supply voltage, such as 3.3V, which is incompatible with integrated circuits using low voltage, thin oxide and small geometry transistor devices to achieve low power consumption and high speed.
One example system application is a PON (Passive Optical Networks) optical module incorporating a laser diode driver and a receiver. The typical optical module requires 3.3V power source as a standard system power supply. The requirement for the standard 3.3V power supply precludes the use of integrated circuits incorporating thin oxide transistors devices to increase the speed of operation of the integrated circuits. In some cases, a system application may use a linear regulator (such as an LDO) to generate a low power supply voltage to supply integrated circuits with thin gate oxide and small geometry devices in order to achieve high speed of operation. However, using an LDO to step down the standard system power supply voltage is not power efficient due to the wasted power drop across the LDO. In other cases, a system application may use a switching regulator to generate a low power supply in order to increase power efficiency. However such approach would require an external inductor that increase cost, and generate switching noise that could be detrimental to analog circuits in the system.